Morphometric analysis of the larval branchial chamber in the dragonfly Aeshna cyanea Muller (Insecta, odonata, anisoptera)

The aquatic larvae of anisopteran dragonflies possess tracheal gills located in the rectum. Using stereological methods, we estimated the morphometric diffusing capacity for oxygen (D-MO2) across the gill epithelium, i.e., from rectal water to the gill tracheoles, in the larvae of Aeshna cyanea. A 271-mg larva has a total branchial surface area of similar to12 cm(2). Tracheoles make up 6% of the epithelial volume of the gills; the harmonic mean thickness of the water-tracheolar diffusion barrier is 0.27 mum and consists mainly of cuticle. The calculated D-MO2 is 23.0 mul min(-1) g(-1) kPa(-1), which, using published values for oxygen consumption in a similar species, would result in a mean driving pressure of 0.2 kPa at rest and 1.3 kPa during activity. Since these driving pressures are similar to those reported for other arthropods, we conclude that the D-MO2 of the gill is not rate-limiting for aerobic metabolism in Aeshna cyanea larvae. (C) 2004 Wiley-Liss, Inc.